[Objectives]  To determine the factors that affect the mating behavior of the gall midge, Gephyraulus lycantha Jiao & Kolesik, a frequent and recurrent pest of Lycium barbarum, in order to provide information to develop techniques controlling of this pest with sex pheromones. [Methods]  The mating behavior of G. lycantha was studied under laboratory conditions and the effects of age and host plant species on mating frequency and duration were statistically analyzed. [Results] Adults generally begin courtship and mate immediately after emerging. Mating behavior has three aspects avoidance, fighting and mating. Both males and females search for, and identify, mates. Copulation has an obvious dynamic, hourly rhythm, which is mainly concentrated in the light phase of the photoperiod, peaking at 2 h (8:00) in the light phase.  The average mating duration of adults was (32.49±1.67) s, with most in the range of 10.0-50.0 s.  Multiple copulation occurred in both male and female adults, but was more common in males.  The frequency of mating by both sexes significantly decreased with age. Host plant species had no significant effect on mating behavior. [Conclusion]  Age is the main factor affecting mating in G. lycantha. These results indicate that it should be both feasible and effective to use sex pheromones to control this pest.